Local application of extracellular matrix proteins fails to reduce
the number of axonal branches after varying reconstructive surgery on rat
facial nerve
Affiliations: Department of Anatomy, University of Cologne, Cologne,
Germany | Department of Oto-Rhino-Laryngology, University of
Cologne, Cologne, Germany | Department of Physiology, Neurophysiology, University
of Bonn, Bonn, Germany | Department of Biochemistry, Institute of Animal
Anatomy and Physiology, University of Bonn, Bonn, Germany
Note: [] Corresponding author: Dr. Doychin N. Angelov, M.D., Ph.D.,
Institut I für Anatomie der Universität zu Köln,
Joseph-Stelzmann-Strasse 9, D50931 Köln, Germany. Tel.: +49 221 478
5654; Fax: +49 221 478 6711; E-mail: angelov.anatomie@uni-koeln.de
Abstract: Purpose: A major reason for the poor functional recovery after
peripheral nerve injury is the outgrowth of supernumerary axonal branches at
the lesion site. Projecting within several nerve fascicles, the branches of one
axon often re-innervate synchronously muscles with antagonis-tic functions and
impair any coordinated activity. We hypothetized that accelerated axonal
elongation through extracellular matrix proteins fos-tering neurite outgrowth
might reduce axonal branching and improve recovery of function. Methods: In a
control group of rats, ramus zygomaticus, ramus buccalis, and ramus marginalis
mandibulae of the facial nerve were transected and the stumps labeled with DiI,
Fluoro-Gold (FG), and Fast Blue (FB). Results: Neuron counts showed that the
zygomatic ramus contained axons of 204 ± 88 DiI-labeled motoneurons in
the dorsal facial subnu-cleus. No perikarya were labeled by 2 or 3 tracers.
After transection and suture of the facial nerve trunk, the zygomatic ramus
contained axons of 328 ± 50 motoneurons dispersed throughout the whole
facial nucleus. The occurrence of double-labeled (DiI+FG and DiI+FB)
motoneu-rons showed that about 30 % of all axons in the zygomatic ramus had a
twin branch projecting within the buccal and/or mandibular ramus. Conclusions:
Entubulation of transected facial nerve in a silicone tube containing phosphate
buffered saline, collagen type I, laminin, fibronectin, or tenascin did not
reduce the portion of double-labeled motoneurons. We conclude that (i) axonal
branching follows a rather con-stant pattern regardless of changes in the local
microenvironment; (ii) despite their known effect to support neurite outgrowth,
all tested extra-cellular matrix proteins do not suppress axonal branching in
the rat facial nerve model.
